When the government's Health and Social Care Bill was finally passed by Parliament last year it was on the condition that GPs would not be forced to open up NHS services to private competition.

Andrew Lansley, the-then Health Secretary, told the Commons: "There is absolutely nothing in the Bill that promotes or permits the transfer of NHS activities to the private sector". In a letter to Clinical Commissioning Groups, he wrote:

I know many of you have read that you will be forced to fragment services, or put them out to tender. This is absolutely not the case. It is a fundamental principle of the Bill that you as commissioners, not the Secretary of State and not regulators – should decide when and how competition should be used to serve your patients interests.

Having accepted Lansley's assurances, the Lib Dems granted the bill their support. But new regulations published under Section 75 of the act flatly contradict the government's promises. The guidelines state that commissioners may only award a contract without competition if they are "satisfied that the services to which the contract relates are capable of being provided only by that provider". In practice, then, GPs will be forced to open up all NHS services to private companies, regardless of the wishes of local people, with the healthcare regulator Monitor granted the power to block any "unnecessary" restriction of competition.

Secondary legislation like this is normally nodded through parliament without debate but Labour, smelling a rat, warned that the regulations amounted to an attempt at backdoor privatisation. Jeremy Hunt, Lansley's replacment as health secretary, initially sought to dismiss the opposition's concerns. In response to a question from Jamie Reed, the shadow health minister, he declared: "Who exactly are the section-75 bogeymen [he] hates: Whizz-Kidz, who are supplying services to disabled children in Tower Hamlets? Or Mind, which is supplying psychological therapy to people in Middlesbrough?"

But after the Lib Dems joined Labour in raising concerns, Hunt has been forced to think again. Norman Lamb, the Lib Dem health minister, told his party colleague Andrew George, one of those opposed to the regulations, "We are looking at this extremely seriously. Clear assurances were given in the other place during the passage of the legislation, and it is important that they are complied with in the regulations."

In reponse, as today's Guardianreports, Hunt has made it clear that he is prepared to rewrite the new guidelines. A source tells the paper: "We are aware that there are concerns over the wording and the way it may be interpreted. We are speaking to the Lib Dem peers to make sure they are happy. We want to make sure everyone is happy."

The shadow health secretary, Andy Burnham, said in response: "The government has been caught out trying to force through privatisation of the NHS by the back door.

"This is another humiliating U-turn to add to the government list, but we believe ministers will stop at nothing to drive through their plans to put the NHS up for sale to the highest bidder."

But will this be anything other than a comestic rewrite? Ahead of the Lib Dems' spring conference next month, this is a key test of the party's nerve.